Installations are known for closing receptacles heat-sealing a length of strip, generally a length of composite strip including a layer of material suitable for welding to the orifice of a receptacle and a layer that forms a barrier against ultraviolet radiation or that provides mechanical strength to the length of strip installed on the orifice of the receptacle.
In such installations, the length of heat-sealable strip is cantilevered out over the orifice of a receptacle, and then a heat-sealing head is lowered to weld the length of strip. A special problem arises when the heat-sealable strip is of insufficient stiffness to enable the length of heat-sealable strip to extend horizontally over the orifice of the receptacle. Under such circumstances, the length of strip tends to droop downwards as soon as it is cantilevered out, and mere friction against the top orifice of the receptacle causes the length of strip to wrinkle so that it does not completely cover the orifice of the receptacle at the moment when the heat-sealing heat is engaged, and as a result the receptacle is not properly closed. To ensure that the orifice of the receptacle is properly covered when using a very fine heat-sealable strip of low stiffness, proposals have therefore been made to install grasping devices that grasp one end of the strip and pull it over the location of a receptacle.
Such devices are complex and use up a considerable amount of strip because of the portion of strip that must be provided to give a grasp to the grasping means.